The commensurate and incommensurate magnetic structures of the magnetoelectric system YMn2O5, as determined from neutron diffraction, were found to be spin-density waves lacking a global center of symmetry. We propose a model, based on a simple magneto-elastic coupling to the lattice, which enables us to predict the polarization based entirely on the observed magnetic structure. Our data accurately reproduce the temperature-dependence of the spontaneous polarization, in particular its sign reversal at the commensurate-incommensurate transition.
@article{arxiv.cond-mat/0511174,
title = {Ferroelectricity induced by acentric spin-density waves in YMn$_2$O$_5$},
author = {L. C. Chapon and P. G. Radaelli and G. R. Blake and S. Park and S-W. Cheong},
journal= {arXiv preprint arXiv:cond-mat/0511174},
year = {2009}
}